Method for monitoring the operation of a doctor assembly in a paper machine and a doctor assembly for implementing the method

ABSTRACT

The operation of a doctor assembly ( 16 ) in a paper machine is monitored. In case of a malfunction, the paper machine&#39;s ( 10 ) control devices ( 14 - 14′, 15 ) are used to carry out the necessary measures for eliminating the malfunction and carrying out repair and/or protective measures. In addition, detector devices ( 20 ) are arranged in connection with the doctor assembly ( 16 ), to detect a malfunction. The detector devices ( 20 ) are connected to the control devices ( 14, 14′, 15 ) of the paper machine ( 10 ), in order to carry out the said measures automatically. The invention also relates to doctor assemblies in a paper machine for implementing the method.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims priority on Finnish Application No. 20010752,Filed Apr. 11, 2001, and is a U.S. National Stage application ofInternational Application No. PCT/FI02/00299, filed Apr. 10, 2002.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

The present invention relates to a method for monitoring the operationof a doctor assembly in a paper machine, a doctor member belonging tothe doctor assembly being used to scrape material off a moving surface.Detector devices are arranged in connection with the doctor assembly andare used to monitor the operation of the doctor assembly and, if thedoctor member drops through, to perform, together with the papermachine's control devices connected to the detector devices, themeasures necessary to run down, before the doctor assembly beingmonitored, the web being manufactured on the paper machine, in order toeliminate the disturbance caused by the drop-through and to performrepair and/or protective measures. The invention also relates to adoctor assembly for implementing the method.

U.S. Pat. No. 5,021,124 discloses a doctor assembly, in which there aretwo doctor blades. An excellent doctoring result can be achieved usingthe disclosed doctor assembly, as individual doctor beams, which can beadjusted together or independently of each other, are arranged for eachdoctor blade. In addition, the construction permits material doctoredoff the surface being doctored with the second doctor blade to beremoved from between the doctor beams. The space is required especiallywhen the paper web is being run down, if the first doctor blade, so tosay, drops through the paper web. In that case, the entire paper webruns between the doctor beams and down into the pulper.

A major problem in the doctor described above, and in others, concernsmalfunctions, in which the doctor assembly does not operate as designed.This is because few malfunctions are noticed in time. Generally, theoperating personnel notices a malfunction quite by accident. Even asmall malfunction, if it continues for a long time, can result in greatdamage to equipment, particularly in the press section of a papermachine. On the other hand, one significant problem in a modernhigh-speed paper machine is precisely the second doctor blade becomingblocked, if the first doctor blade drops through. A large amount ofmaterial then rapidly collects on top of the doctor beams, and can evenbend them. In any event, cleaning the doctor assembly is laborious,despite the washing sprays. A corresponding situation occurs, if thepulper malfunctions and the doctored material collects in the doctorassembly, bending the doctor beams. Both doctor blades can then dropthrough. Dropping through and a poor doctoring result are alsodisadvantageous to the operation of doctors located in other positionstoo. Using the state of the art it is, however, practically impossibleto detect malfunctions and prevent damage.

European patent application number 989234 discloses a doctor, which isused to scrape a press roll. In this doctor, the angle of the bladeholder or the doctor blade is monitored by means of sensors, which areconnected to the control of the pick-up roll. For example, a suddenchange in the angle of the blade holder is detected as a malfunction, inwhich case the pick-up roll is raised to avoid damage to the press.However, it is impossible to use the arrangement disclosed to detect adrop through, or other malfunctions of the doctor.

In a drop through, there is, after the doctor blade, material on thesurface being doctored, which remains unnoticed when monitoring theangle. Thus, the assembly disclosed is mainly only suitable fordetecting foreign bodies and random accumulations of material on thepress. The assembly will also easily give false alarms, if it is set todetect very small changes in angle or position. Correspondingly, if theassembly reacts only to large changes, it will be too late to preventdamage.

SUMMARY OF THE INVENTION

The invention is intended to create a new type of method for monitoringthe operation of a doctor assembly in a paper machine, by means of whichmalfunctions, such as particularly a drop through, can be detected andcorrected, and/or protective measures can be taken easily and above allrapidly. The invention is also intended to create a new type of doctorassembly in a paper machine, which will allow various kinds ofmalfunction to be detected rapidly, thus avoiding further damage causedby malfunctions.

In the doctor assembly according to the invention, there are specialdevices for monitoring the operation of the doctor assembly. Thesedevices are arranged to react to a malfunction, making it possible tominimize further damage caused by the malfunction. In addition, if amalfunction occurs, the information available from the devices can beutilized when carrying out repair and/or protective measures. Thenecessary measures can be easily incorporated in the control of thepaper machine, so that especially in critical positions at least theinitial measures for avoiding further damage are wholly automatic. Themethod according to the invention can be easily applied to existingpaper machines. In addition, the method can be used to improve theutilization of a paper machine.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is examined in detail with reference tothe accompanying drawings depicting some embodiments of the invention,in which:

FIG. 1 shows a schematic diagram of the doctor assembly according to theinvention applied to a paper machine, as well as of the control devicesof the paper machine.

FIG. 2 shows a side view of the doctor assembly according to theinvention applied in connection with a roll.

FIG. 3 shows a perspective view and cross-section of part of the doctorassembly of FIG. 2.

FIG. 4 shows a schematic diagram of a second embodiment of the doctorassembly according to the invention.

FIG. 5 shows a schematic diagram of a third embodiment of the doctorassembly according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a schematic diagram of a paper machine 10, that is, assuch, known. In this case, the term paper machine also refers to a boardmachine or similar. In FIG. 1, the paper machine 10 is divided intothree sub-totalities. The first of these, in the production direction ofthe paper machine 10, is the web formation section 11, the second beingthe press section 12, followed by the drying section 13 with thefinishing equipment. Modern paper machines incorporate a great deal ofhighly developed control equipment. For reasons of clarity, the controldevices 14-14″ in FIG. 1 are shown schematically as being separate fromeach sub-totality 11-13. The control devices include, for instance,various sensors and the meters connected to them, as well as operatingdevices and the means required to control them.

Nowadays all, or at least most of the control devices 14-14″ also arefurther connected to form a control centre 15, allowing the entire papermachine to be monitored and controlled centrally from a single location,such as a control room.

The doctor assembly 16 according to the invention is intended to scrapea moving surface 17 (FIG. 2). In a paper machine, the surface beingdoctored is usually the surface of a roll 17′ or a belt. In the doctorassembly in question, there is at least one doctor member 18, which isin practice generally a doctor blade 18′, arranged in contact with thesurface 17. The doctor member 18 is used to scrape the moving surface 17and thus remove material used in the paper machine from the surface. Thematerial can be, for instance, fine material that adheres to the surfaceof a roll during production. Doctoring with the doctor member thus keepsthe surface of the roll clean. However, the material can also be thepaper web 19 itself, which is doctored off the surface of the roll 17,for example, during so-called running down (FIG. 2). FIG. 1 shows adoctor assembly 16, which is fitted to the press section, as larger thanit really is. The rolls forming the press nip are not shown, but inpractice the doctor assembly 16 shown is located below the lowest roll17′ of the relevant rolls, according to FIG. 2. In this case, the doctorassembly 16 is formed of two doctor beams 16′ and 16″ with doctor blades18′ and 18″ fitted to them. Besides the press rolls, other criticaldoctor assemblies are located in connection with the transfer belts andthe first and last dryer rolls.

To prevent damage and production losses, detector devices 20 arearranged in connection with the doctor assembly 16, to detect anymalfunction of the doctor assembly. The most serious malfunctions are apoor doctoring effect by the doctor blade and a drop through. Accordingto the invention, the detector devices 20 can be of many differentkinds, but each of them is connected to the control devices 14-14′ ofthe paper machine 10, for carrying out repair and/or protectivemeasures. A message of a malfunction given by the detector devices canbe converted into a signal, for example to the control room, so that therequisite measures can be started immediately. The control devices canalso be set to carry out specific measures immediately a message isreceived, as manual repair and/or protective measures are often tooslow. Thus, the most critical measures take place automatically. Suchmeasures include, especially in the press section, raising the pick-uproll, lightening the nip load, and opening the doctors. Raising thepick-up roll will run the web down between the web formation section andthe press section, thus preventing the web traveling on to a doctorassembly that has dropped through. A web break and running down can beaccelerated by releasing the vacuum from the pick-up roll.Correspondingly, excess pressure can be lead to the pick-up roll. Thenecessary measures can also be easily programmed to form a specificsequence, making most operations simultaneous. The malfunction can thenbe eliminated as quickly as possible, without damaging neighbouringstructures. This also shortens the production break caused by themalfunction. The detector devices 20 can be connected to the controldevices 14-14″ or to the control center 15, either over a permanentconnection, or wirelessly, as depicted by a broken line in FIG. 1.

Generally, the detector devices are arranged after the doctor member, inthe direction of travel of the moving surface. The detector devices canthen be used to detect if the doctor member has dropped through, or ifits doctoring effect is poor. Normally there is no material on thesurface after the doctor member. Similarly, for example, with a doubledoctor in the press section it will be detected if the pulper isbecoming full for some reason. In a double doctor, detector devices arealso preferably fitted after the second doctor blade (FIG. 2). This willdetect a malfunction in which both doctor blades drop through. Thoughthis case is certainly unusual, it generally causes great damage. Thisis because if both doctor blades drop through, the paper web will winditself around the roll. FIG. 2 shows the first doctor blade 18′ of thedoctor assembly 16 at the moment it drops through. The paper web 19 thenstrikes the second doctor blade 18″ and leaves the surface of the roll17′, to strike the detector devices 20. Normally, when running down, thefirst doctor blade 18′ detaches the paper web 19, creating the situationshown by the broken line in FIG. 2. The same reference numbers are usedfor functionally similar components.

The following describes various detector devices and their operation.Detector devices operating on different principles can be fitted to thesame doctor assembly, thus achieving good operating reliability andavoiding false alarms. In addition, measures are preferably taken onlyif a malfunction is detected by two detector devices of different types.It is also preferable to place several detector devices of the same typein the same doctor assembly, as this will improve the reliability of thedetector devices. According to the invention, the detector devices areformed of contact-less members, such as optical, acoustic, or othersimilar members. The said members are fitted to one or both ends of thedoctor assembly. The members can also be located at, for instance,suitable intervals over the entire length of the doctor assembly. Inpractice, the optical members are arranged to react to materialappearing during a malfunction, on the moving surface and/or on top ofthe doctor assembly. Detection can be implemented in several differentways. One way is to use photocells placed at both ends of the doctorassembly. In that case, if a malfunction occurs, the material collectingon the doctor assembly will break the beam between the photocells,causing a signal to be transmitted to the control devices of the papermachine. FIG. 3 shows the transmitter photocell 21 and the beam 21′ sentby it. The light used can be visible light, a laser beam, or infrared orother light with a specific wavelength. In addition, at the other end ofthe doctor assembly, it is possible to arrange simply a reflector,which, however, will make the system more liable to malfunction than theprevious arrangement. Optical sensors can also be advantageouslyinstalled in a tubular casing, which will prevent them from dirtying(FIG. 3). Despite the need for the casing, photocells and other similaroptical sensors are small and economical.

Various cameras, which react to changes in tone or shape are alsosuitable for use as optical sensors. In particular, this will make itpossible to be certain that the paper web is in place, as a paper web isgenerally considerably lighter in tone, than, for example, the surfaceof a roll. Reliability can be improved by lighting with a light that isreflected by the fillers in the paper web. This is an especially goodway of detecting a drop through of the second doctor blade. In addition,it is possible to use machine vision, which can be calibrated to aspecific normal situation. If a malfunction occurs, the machine visiondetects that the situation has changed and gives an alarm. Machinevision is also suitable for the longer term monitoring of the operationof the doctor assembly. It is then possible to detect the gradualdirtying or wear of the surface being doctored, making it easier to planmaintenance shutdowns. FIG. 3 shows only one camera 22, though there canbe several, if necessary.

In case of a malfunction, the sound around the doctor assembly alsochanges. The acoustic members used will then react to the sound causedby the malfunction. At their simplest, the acoustic members comprise oneor more microphones, which are set to a specific noise level, levelsabove which cause the apparatus to give a signal of a malfunction.However, sound of a specific frequency may even diminish during amalfunction. Ultrasound sensors are also appropriate. These can be usedto detect not the sound level, but the material. Modern ultrasoundsensors are cheap, simple, and fast. It is preferable to use a so-calleddirectional microphone 23, according to FIG. 3, as the microphone, orelse a microphone used in so-called acoustic emission measurement, whichif attached to the doctor beam, blade holder, or doctor blade will reactto sound traveling in these structures.

Though most of the aforementioned detector devices are small in size andreliable in operation, they will require calibration according to theircurrent operating environment.

The detector devices according to the invention can also be mechanicalmembers, fitted in the area between the ends of the doctor assembly.Some of the members can be installed outside of and in connection withthe ends (FIG. 3), which will facilitate installation and maintenance.In addition, mechanical members are arranged to react to the force ofthe material collecting on them during a malfunction. Thus, they can beeasily manufactured to suit many different kinds of doctor assembly.Generally, the mechanical members include one or several state sensors24 with a projection 24′ attached, on top of which material is intendedto collect to operate the state sensor 24. FIGS. 2 and 3 show threedifferent mechanical members. The first is a cable 25 stretched betweenthe ends of the doctor assembly 16, with one end attached to a suitablesensor construction 25′. Besides a cable, it is also possible to use,for example, a wire or similar thin member. If the first doctor blade18′ drops through, the paper web 19 will strike the suitably positionedcable 25, signaling a malfunction (FIG. 2). The cable 25 is preferablyintended not to break, so that it only needs to be installed once.Alternatively, it is possible to use a thinner fibre, or for example anelectrical conductor 26, the breaking of which signals a malfunction.The conductor 26 itself then forms both the projection and the statesensor. Further, instead of a cable, it is possible to use a thin shaft27, with suitable barbs 27′ attached, according to FIG. 2. A malfunctionis then detected on the basis, not of bending, but of the rotation ofthe shaft 27, which is detected using an angle sensor (not shown) set onthe shaft 27. The mechanical members described above extend over theentire distance of the doctor assembly. Due to the long distance, theirconstructions must be dimensioned strongly and their installation may belaborious. Small and light constructions can be advantageously used byinstalling several state sensors 24 at suitable intervals on the doctorbeam 18′. The mechanical member shown in FIG. 2 operates in the mannerdescribed. A projection 24′ is attached to the state sensor 24, and isstruck by the paper web 19 in case of a malfunction. As the mechanicalmembers referred to above are round and thin, practically no finematerial collects on top of them. This avoids false alarms.

Nearly all of the detector devices described above are based primarilyon the detection of material during a malfunction. In addition to them,it is possible to use detector devices that are adapted to react to achange in some physical quantity in the doctor assembly that resultsfrom a malfunction. Especially if several sensors operating on differentprinciples are used, a malfunction will be detected rapidly andcertainly, while at the same time avoiding false alarms. According tothe invention, the detector devices are sensors, which react to thedoctor assembly's temperature, pressure, vibration, mass, electricalconductivity, capacitance, or other physical quantity. For example, in adrop-through situation, a temperature sensor located after the doctorblade will detect a relatively warm paper web. The same temperaturesensor can also react to the temperature of the roll. In case of amalfunction, the doctor assembly generally also vibrates noticeably.FIGS. 2 and 3 show different kinds of sensor. An increase in mass can bedetected using, for example, strain sensors 28 connected to the bearings30 of the doctor assembly 16. Correspondingly, electrical conductivityor capacitance will change if a damp paper web collects on top of thedoctor beams 16 and 16′, such a change being detected by a measurementsensor 29 fitted to the doctor beam 16′.

FIG. 4 shows a schematic diagram of a doctor assembly 16, a malfunctionof which can be detected using detector devices 20 located in connectionwith the doctor assembly 16. The doctor assembly 16 also includesdevices 31 arranged to detect the normal situation in the paper machine.In the normal situation, the web travels without disturbance. The pathof travel of the web is shown in FIG. 4 by a line of alternating dashesand dots. The said devices 31 can be, for example, laser distance meters31′ which are used to detect the point where the web detaches. Accordingto the invention, the devices 31 are connected to detector devices 20,which are fitted before the doctor member 18 in the direction of travelof the moving surface 17, and which are arranged, during a malfunctiondetected by the devices 31, to detect the absence of material before thedoctor member 18, in order to detect a malfunction of the doctorassembly 16. In other words, if the web breaks, the material is removedby the doctor member 18. The web 19 will then drop according to the wavyline (FIG. 4). According to the invention, following a clear change inthe point of detachment, the presence of material is monitored beforethe doctor member and especially below it. For this purpose, severaldetector members 20, at the various locations shown by the crosses inFIG. 4, are arranged in the doctor assembly 16. Generally, it ispreferable for both the devices and the detector members to monitor thesituation continuously. If the devices signal that the point ofdetachment is deviating, or that it is totally missing, and if thedetector devices do not detect material, i.e. a dropping web, it ishighly probable that the doctor assembly is malfunctioning. Thenecessary measures can then be carried out to eliminate the malfunction,as described previously.

FIG. 5 shows a variation of the previous embodiment. In this case,detector members 31″, which are arranged at the exit point of thematerial 19 to be removed, such as the pulper feed opening 32, are usedas the devices 31. The detector members can also be in connection withthe doctor member 18, or at both locations. If the pick-up roll istransferring the web to the press section, but the web is detected to bemissing at the dryer section, the web 19 will be normally run down intothe pulper, according to FIG. 5. The web 19 will then strike one of thedetector members 31″, showing that the doctor assembly is operatingcorrectly. Correspondingly, if the doctor assembly 16 malfunctions, thedetector members 31″ will remain in the ready position, so that theabsence of the material will be detected. In FIG. 5, the detectormembers 31″ are shown in the ready position, their operating positionbeing correspondingly shown by broken lines. The detector members can bemechanical, optical, and/or acoustic, as described above. In addition,the devices and members depicted in the description can be combined inthe same position, which will increase the certainty of a malfunctionbeing detected and also reduce the number of false alarms.

In the prior art, the only way to monitor the operation of a doctorassembly is mainly to stand next to it and watch it. Due to the largenumbers of doctor assemblies, it is totally impossible to monitor theoperation of each one continuously. In practice, malfunctions are mainlynoticed by accident, usually by their sound, after which the papermachine's control devices are used to perform the necessary measures toeliminate the malfunction and carry out repair and/or protectivemeasures. According to the invention, detector devices are arranged inconnection with the doctor assembly to detect a malfunction and are alsoconnected to the paper machine's control devices, to carry out the saidmeasures automatically. This makes it possible, if desired, tocontinuously monitor each doctor assembly and also to largely avoid thedamage caused by a malfunction. The detector devices are preferablylocated in connection with a double doctor forming a doctor assembly andparticularly in the space between the first and second doctor members.This means that a drop through of particularly the first doctor bladewill be detected. Further, detector devices are located in connectionwith a double doctor forming a doctor assembly in the press section of apaper machine. This will bring significant benefits, as this particulardoctor assembly is known to be one of the most critical.

By means of the detector devices and/or members connected to it, thedoctor assembly according to the invention will help to increase theutilization of a paper machine. By detecting malfunctions and using thecontrol devices to carry out repair and/or protective measures, furtherdamage will be effectively prevented. Use of the detector devices and/ormembers makes it possible to continuously monitor the operation of thedoctor assembly, so that it will even be possible to predictmalfunctions. According to the invention, the primary monitoring is ofthe situation after the doctor member, so that it is possible to detectnumerous different malfunctions. The observations can be usedsecondarily to determine the condition of the doctor member,facilitating the planning of maintenance shutdowns. However, what isimportant is that the monitoring is continuous and the repair and/orprotective measures are essentially carried out automatically. Besidesthe automated performance of repair and/or protective measures, thesecan also be carried out manually, if necessary, though this is often tooslow, however. The detector devices and/or members and method accordingto the invention can easily be applied in various doctor assemblies.These include not only double doctors, but other doctors, in which thesurface being doctored is usually a roll or a belt, such as a transferbelt.

1. A method for monitoring the operation of a doctor assembly having afirst doctor member, in a paper machine making a paper web, the methodcomprising the steps of: scraping material or the paper web off a movingsurface which moves in the machine direction, with the first doctormember; monitoring the moving surface directly with an optical memberafter the moving surface has passed the first doctor member in themachine direction, and checking with the optical member for the materialor the paper web present on the moving surface; and when the opticalmember detects the material or the paper web present on the movingsurface carrying out, with paper machine control devices connected tothe detector devices, running down the web being manufactured on thepaper machine, before the first doctor member, in order to eliminate themalfunction caused by the drop-through and to carry out repair and/orprotective measures.
 2. The method of claim 1, wherein the doctorassembly includes the first doctor member and a second doctor member,and wherein the step of monitoring the moving surface directly with anoptical member comprises using an optical member located after thesecond doctor member.
 3. The method of claim 2, further comprising usingthe double doctor assembly in a press section of the paper machine. 4.The method of claim 2, further comprising directing a light that isreflected by fillers in the paper web at the moving surface, after themoving surface has passed the first doctor member, and detecting saidlight with the optical member.
 5. The method of claim 2, wherein theoptical member is a camera, further comprising using the camera tomonitor the moving surface for a change from a darker to a lighter toneto detect the material or the paper web present.
 6. The method of claim2, wherein the optical member is a camera, and further comprising usingthe camera with machine vision to calibrate a specific normal situation,and to detect the material or the paper web present by a change in thespecific normal situation.
 7. The method of claim 2, wherein the step ofmonitoring the moving surface directly comprises monitoring the movingsurface directly with a plurality of optical members.
 8. The method ofclaim 1, wherein the step of running down the web being manufactured onthe paper machine, comprises at least one measure taken from the groupconsisting of: rasing a pick-up roll, releasing vacuum from a pick-uproll, creating excess pressure in the pick-up roll, or releasing aloading pressure from the doctor assembly.
 9. A method for monitoringthe operation of a doctor assembly having a first doctor member, in apaper machine making a paper web, the method comprising the steps of:scraping material or the paper web off a moving surface which moves inthe machine direction, with the first doctor member; monitoring themoving surface directly with a temperature sensor after the movingsurface has passed the first doctor member in the machine direction, andchecking with the temperature sensor for the material or the paper webpresent on the moving surface; and when the temperature sensor detectsthe material or the paper web present on the moving surface carryingout, with paper machine control devices connected to the detectordevices, running down the web being manufactured on the paper machine,before the first doctor member, in order to eliminate the malfunctioncaused by the drop-through and to carry out repair and/or protectivemeasures; wherein the temperature sensor reacts to a change intemperature, detecting a warm paper web or reacting to the temperatureof the roll.
 10. A method for monitoring the operation of a doctorassembly having a doctor beam and a first doctor member mounted to thedoctor beam, in a paper machine making a paper web, the methodcomprising the steps of: scraping material or the paper web off a movingsurface which moves in a machine direction, with the first doctormember; monitoring the material or the paper web collecting on thedoctor beam during a malfunction downstream of the first doctor memberwith a plurality of mechanical state sensors, having projectionsarranged so that during a malfunction the material or the paper webcollects on said projections such that the plurality of mechanical statesensors react to force caused by the material or the web collecting onthem during malfunctions; and when the plurality of mechanical statesensors detect the material or the paper web collecting on saidprojections, carrying out, with paper machine control devices connectedto the plurality of mechanical state sensors, running down the web,before the first doctor member, in order to eliminate a malfunctioncaused by a drop-through of the first doctor member.
 11. A method formonitoring the operation of a doctor assembly having a first doctormember including a doctor beam, a doctor holder and a doctor blade, in apaper machine making a paper web, the method comprising the steps of:scraping material or the paper web off a moving surface which moves in amachine direction, with the first doctor member; monitoring amalfunction of the first doctor member with acoustic members which reactto sound; and when the acoustic members detect a change in sound,carrying out, with paper machine control devices connected to thedetector devices, running down the web, before the first doctor member,in order to eliminate a malfunction caused by a drop-through of thefirst doctor member.
 12. The method of claim 11, wherein the step ofmonitoring the malfunction of the first doctor member comprises:preforming acoustic emission measurement, with a microphone attached tothe doctor beam, blade holder, or doctor blade and detecting soundtraveling in said doctor beam, blade holder, or doctor blade.
 13. Themethod of claim 12, wherein the acoustic emission measurement ispreformed with respect to ultrasound.
 14. A method for monitoring theoperation of a doctor assembly having a first doctor member, in a papermachine making a paper web, the method comprising the steps of: scrapingthe paper web off a moving surface which moves in a machine direction,with the first doctor member; monitoring the moving surface with firstdetector devices arranged upstream in the machine direction from thefirst doctor member, to detect the paper web on the moving surfaceupstream of the first doctor member to thus detect normal operation ofthe paper machine up to the first doctor member; monitoring with seconddetector devices spaced from the first doctor member in an upstreamdirection, the presence of the paper web below the first doctor memberwhich paper web has been removed from the moving surface; and whereinwhen the paper web is present upstream of the first doctor member butnot present below the first doctor member and thus is detected amalfunction of the first doctor assembly, carrying out, with papermachine control devices connected to the detector devices, running downthe web, before the first doctor assembly, in order to eliminate themalfunction caused by a drop-through of the first doctor member.
 15. Amethod for monitoring the operation of a doctor assembly having a firstend and a second end, the doctor assembly having a doctor beam, thedoctor beam extending between the doctor assembly first end and secondend, and a first doctor member mounted to the doctor beam, in a papermachine making a paper web, the method comprising the steps of: scrapingmaterial or the paper web off a moving surface which moves in a machinedirection, with the first doctor member; monitoring the material or thepaper web collecting on the doctor beam during a malfunction downstreamof the first doctor member with a thin member extending between thefirst end and the second end of the doctor assembly so that during amalfunction the material or the paper web collects on said thin member,and activates a sensor attached to an end of the thin member; and whenthe sensor detects the material or the paper web collecting on said thinmember carrying out, with control devices in the paper machine which areconnected to said sensor, running down the web, before the first doctormember, in order to eliminate a malfunction caused by a drop-through ofthe first doctor member.
 16. The method of claim 15 wherein the thinmember is a shaft which is rotated by the material or the paper webcollecting on the doctor beam, and further comprising the step ofmonitoring the material or the paper web collecting on the doctor beamby monitoring said rotation.
 17. The method of claim 15 wherein the thinmember is a shaft which is rotated by the material or the paper webcollecting on the doctor beam, said rotation detected using an anglesensor set on the shaft.
 18. A method for monitoring the operation of adoctor assembly having a first end and a second end, the doctor assemblyhaving a doctor beam, the doctor beam extending between the doctorassembly first end and second end, and a first doctor member mounted tothe doctor beam, in a paper machine making a paper web, the methodcomprising the steps of: scraping material or the paper web off a movingsurface which moves in a machine direction, with the first doctormember; monitoring the material or the paper web collecting on thedoctor beam during a malfunction downstream of the first doctor memberwith a beam of light so that during a malfunction the material or thepaper web collects on said doctor beam, and breaks said beam of lightwhich is detected by a sensor; and when the sensor detects the lightbeam is broken, with control devices in the paper machine which areconnected to said sensor, running down the web, before the first doctormember, in order to eliminate a malfunction caused by a drop-through ofthe first doctor member.
 19. The method of claim 18 wherein the beam oflight extends between the first end and the second end of the doctorassembly.
 20. The method of claim 18 wherein the beam of light extendsbetween photocells.
 21. The method of claim 18 wherein the beam of lightis a laser light beam.
 22. A method for monitoring the operation of adoctor assembly having a first end and a second end, the doctor assemblyhaving a doctor beam, the doctor beam extending between the doctorassembly first end and second end, and a first doctor member mounted tothe doctor beam, in a paper machine making a paper web, the methodcomprising the steps of: scraping a moving surface which moves in amachine direction, with the first doctor member to remove the paper web;monitoring a pulper feed opening positioned below the first doctormember to receive the paper web removed from the moving surface, todetect the presence of the paper web in the pulper feed opening;monitoring the presence of the paper web in a dryer section after thedoctor assembly in the paper machine; and if the web is not present inthe dryer section and the paper web is not detected in the pulper feedopening, using control devices connected to the paper machine to rundown the web, before the first doctor member, in order to eliminate amalfunction caused by a drop-through of the first doctor member.
 23. Amethod for monitoring the operation of a doctor assembly having a firstend and a second end, the doctor assembly having a doctor beam, thedoctor beam extending between the doctor assembly first end and secondend, and a first doctor member mounted to the doctor beam, in a papermachine making a paper web, the method comprising the steps of: scrapingmaterial or the paper web off a moving surface which moves in a machinedirection, with the first doctor member; monitoring the material or thepaper web collecting on the doctor beam during a malfunction downstreamof the first doctor member with a measurement sensor fitted to thedoctor beam so that during a malfunction the material or the paper webcollects on said doctor beam and changes the electrical conductivity orcapacitance of the doctor beam said change being detected by saidmeasurement sensor; and when the measurement sensor detects changes inthe electrical conductivity or the capacitance of the doctor beam, withcontrol devices in the paper machine which are connected to said sensor,running down the web, before the first doctor member, in order toeliminate a malfunction caused by a drop-through of the first doctormember.
 24. A method for monitoring the operation of a doctor assembly,having a first end and a second end, the doctor assembly having a doctorbeam, the doctor beam extending between the doctor assembly first endand second end, and a first doctor member mounted to the doctor beam, ina paper machine making a paper web, the method comprising the steps of:scraping material or the paper web off a moving surface which moves in amachine direction, with the first doctor member; monitoring the materialor the paper web collecting on the doctor beam during a malfunctiondownstream of the first doctor member with mass measuring sensors fittedto the doctor beam so that during a malfunction the material or thepaper web collects on said doctor beam and changes the mass of thedoctor beam, said mass being detected by said mass measurement sensors;and when the measurement sensor detects a change in the mass of thedoctor beam, with control devices in the paper machine which areconnected to said sensors, running down the web, before the first doctormember, in order to eliminate a malfunction caused by a drop-through ofthe first doctor member.
 25. The method of claim 24 wherein the doctorassembly is mounted to the paper machine by bearings, and the masssensors are strain sensor connected to the bearings of the doctorassembly, and wherein the step of monitoring the material or the paperweb collecting on the doctor beam comprises measuring the output of thestrain sensors.